Voltage or current spikes (energy spikes) or voltage or current pulses, such as voltage or current pulses caused by electrostatic discharge (ESD) events or by electrical overstress (EOS) may cause damages or reliability problems in semiconductor devices or in integrated circuits (ICs) that include several semiconductor devices. In an ESD process electric charge is transferred in a short time from an object, such as a charged person, a charged electrical cable, or charged manufacturing equipment, to a circuit node connected to the semiconductor device or the IC. A voltage or current spike may damage or destroy the semiconductor device or the IC. Damages induced by voltage or current spikes are, for example, interruption of a connection line by melting the connection line; failure caused by thermal semiconductor junction burn-out; or destruction or degradation of a gate oxide of a semiconductor device such as MOSFET (Metal-Oxide Field-Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor).
Different concepts are known for protecting semiconductor devices or ICs against energy spikes, such as voltage or current spikes resulting from ESD events. According to a first concept, at least one diode, such as a Zener diode or an avalanche diode is connected in parallel to the semiconductor device or IC that is to be protected. For ESD protection purposes the diode is operated in reverse-bias mode and breaks down when a voltage spike occurs that has an amplitude higher than a voltage blocking capability of the diode. When the diode breaks down it conducts a current resulting from an ESD event and protects the semiconductor device or IC against overvoltages by clamping the voltage to a safe level.
According to a further concept, a transistor, such as a MOSFET or an IGBT, has its load path connected in parallel to the semiconductor device or the IC to be protected. Further, a control circuit is connected in parallel to the load path of the transistor and is configured to control (drive in the on-state) the transistor when the voltage across the load path reaches a given voltage threshold. In the on-state, the transistor provides a low-ohmic current path for conducting the current occurring in connection with the ESD event. Transistors usually have an electrical safe operating area (eSOA) that defines the load currents and the corresponding load voltages at which the transistor can be safely operated. The control circuit should, therefore, be implemented such that the transistor is not operated outside the eSOA.